You might install the new OPTs one by one, but two other things have happened since the old forums at TF.n went offline:

Darksaber has released his Ultimate Craft Pack Version 2 (now in revision 2.1), which not only includes most of the "upgrades" (the Zero-G trooper and Space Worker might not be in it), but also many add-on craft, including all of the OPTs of craft from the Clone Wars period. Find the new UCP at http://www.darksaber.pnma.co.uk (and look for the UCP banner on the front page)

Or maybe you don't want any "add-on" craft. This is also OK, because there is now the XWA Upgrade Project Craft Pack, which includes only XWAUP models. Find it at http://www.xwaupgrade.com in the Downloads section.